Stringed musical instrument with electrical feedback

ABSTRACT

This application discloses a stringed musical instrument including a means responsive to the vibrations of a string as it is plucked or hit, and a means for driving the oscillations of the string electromechanically. The means responsive to the vibration generates an electrical signal which is amplified and supplied to the driving means which causes continued vibration of the string. Means are disclosed wherein the string&#39;&#39;s vibrations can be sustained for an arbitrary period of time at its fundamental frequency or at higher harmonics thereof, or at a mixture of fundamental and harmonics, producing a sound rich in overtones unique to this instrument. Also disclosed are means whereby the player selects at will which of a plurality of strings will be driven continuously as drones, which will be driven only when played upon, and which will remain undriven. The effect is to make possible the creation of aesthetically pleasing sounds which are entirely different than those created by standard stringed instruments.

United States Patent [191 Cohen 1 June 26, 1973 STRINGED MUSICALINSTRUMENT WITH ELECTRICAL FEEDBACK [76] Inventor: Marcus S. Cohen, 134Woodland Avenue, Winnetka, 111. 60093 [22] Filed: Apr. 28, 1971 [21]Appl. No.: 138,213

[52] U.S. Cl 84/1.04, 84/l.06, 84/1.16, 84/1.15, 84/1.19 [51] Int. Cl.G0lh 3/00 [58] Field of Search 84/1.l3-1.16, 1.26, 84/1.06, 1.19,267,1.04; 323/22 [56] References Cited UNITED STATES PATENTS R26,533 3/1969Cookerly et a1. 84/1.l5 X 1,838,886 12/1931 Tuininga 84/1.15 2,119,5846/1938 Knoblaugh... 84/1.l5 2,896,491 7/1959 Lover 84/l.l5 3,177,2834/1965 Fender ..84/1.15 X 3,291,888 12/1966 Meazz et a1 84/1.163,325,580 6/1967 Barcus et a1. 84/1.16 3,456,063 7/1969 Teranishi etal.... 84/1.16 3,493,669 2/1970 Elbrecht et a1. 84/1.16 2,784,631 3/1957Fender 84/l.15 2,600,870 6/1952 Hathaway et a1. 84/1.l6 X 3,185,7555/1965 Williams et a1, 84/l.16 X 3,551,787 12/1970 Walters 323/22FOREIGN PATENTS OR APPLICATIONS 673,375 6/1930 France 84/l.l5

Primary Examiner-Richard B. Wilkinson Assistant Examiner-U. WeldonAtlomeyMcDougal1, Hersh & Scott [57] ABSTRACT This application disclosesa stringed musical instrument including a means responsive to thevibrations of a string as it is plucked or hit, and a means for drivingthe oscillations of the string electromechanically. The means responsiveto the vibration generates an electrical signal which is amplified andsupplied to the driving means which causes continued vibration of thestring. Means are disclosed wherein the strings vibrations can besustained for an arbitrary period of time at its fundamental frequencyor at higher harmonics thereof, or at a mixture of fundamental andharmonics, producing a sound rich in overtones unique to thisinstrument. Also disclosed are means whereby the player selects at willwhich of a plurality of strings will be driven continuously as drones,which will be driven only when played upon, and which will remainundriven. The effect is to make possible the creation of aestheticallypleasing sounds which are entirely different than those created bystandard stringed instruments.

11 Claims, 8 Drawing Figures PATENTEDJUNZS 191s 3; 742.1 13

sum 1 or a FIG, 1 4

INVENI'OR 4 977201712215 Sg'oherz, dziys STRINGED MUSICAL INSTRUMENTWITH ELECTRICAL FEEDBACK BACKGROUND OF THE INVENTION This inventionrelates generally to stringed musical instruments. More specifically, itrelates to a musical instrument using feedback to enhance or change thecharacteristic sound of the instrument.

Stringed musical instruments such as guitars, banjos, pianos,harpsichords or the like all havecharacteristic sounds which have eachfit into their own musical tradition. Contemporary musicians have soughtand are seeking to achieve effects which are different from those towhich audiences are accustomed. These efforts are generally welcomed andhave resulted in the creation of new musical forms and techniques.

A particular instrument wherein this effect has been extensive is theguitar. With the advent of electrical amplification it has becomepossible to produce sounds from a guitar which are substantiallydifferent than those produced by conventional unamplified instruments.For instance, to the distress of some, but welcomed by others, it ispossible by substantial amplification of a guitar to achieve a kind ofacoustical feedback and in doing so change the basic sounds produced bythe instrument. Acoustical feedback occurs when the energy in the soundoutput of the speakers strikes the strings, driving their vibrations,and if the sound output is high enough the vibration of the string willbe sustained, or other strings induced to vibrate sympathetically. Thevibration sustained or induced may be at the fundamental frequency or atsome harmonic component thereof. Some novel and aesthetic sounds can beproduced in this manner, but the effect is hard to control by theplayer, ,varies with the pitch of the note being played, and relies onextremely high volume which is displeasing to many and distorts thesound in unpleasant ways. It is impossible to integrate an instrumentrelying on acoustical feedback into a symphony orchestra or any othergroup of acoustical instruments, due to the discrepancy in volume.

This invention provides a new and aesthetic sound comprised of theindefinite sustainance of notes and the generation of harmonics, whichrelies on the principle of electromechanical rather than acousticalfeedback and hence is liberated from the necessity for high volumes. Itcan as easily play with a chamber group as with an electric band;indeed, as the instrument can produce a sound similar to the violin,cello, or both playing together an octave apart, or can imitate thesound of the Indian sitar, it is believed it will gain acceptance as anorchestral instrument with musicians and audiences alike.

Therefore, it is an object of this invention to provide a novel musicalinstrument which is capable of producing new and pleasing musicalsounds.

It is another object of this invention to provide a novel musicalinstrument which can be selectively played so as to produce conventionalmusical sounds or to produce a wide range of novel musical sounds.

It is a further object of this invention to provide a novel musicalinstrument which can produce new and unusual musical effects withoutsuffering from the disadvantage of having to be played at volumes whichmay be unsatisfying or even unpleasant to some.

It is a still further object of this invention to provide a novelmusical instrument which is similar in method of playing to conventionalmusical instruments but is capable of producing awide range of novel andaesthetically pleasing musical sounds.

SUMMARY OF THE INVENTION The foregoing and other objects are achieved inone embodiment of the invention wherein a pickup is provided whichproduces a varying electrical signal in response to the vibration of astring. The electrical signal is then amplified and supplied to a meansfor driving or vibrating the string at the fundamental frequency of thesignal, at some selected harmonic component thereof, or at a mixture ofthe fundamental and its higher harmonics.

BRIEF DESCRIPTION OF THE DRAWING The invention itself is set forth inthe claims appended hereto and forming a part of this specification. Thestructure and mode of operation of various embodiments thereof may beunderstood by reference to the detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a plan view of a guitar embodying this invention;

FIG. 2 is a schematic illustration of one embodiment of the invention;

FIG. 3 is a schematic illustration of a second embodiment of theinvention;

FIG. 4 is a schematic illustration of a third embodiment of theinvention;

FIG. 5 is a schematic illustration of a fourth embodiment of theinvention;

FIG. 6 is a schematic illustration of another embodi ment of theinvention;

FIG. 7 is a circuit diagram of still another embodiment of the inventionas included in the guitar of FIG. 1; and

FIG. 8 is a sectional view of an embodiment of the driving means forminga part of the invention.

DETAILED DESCRIPTION FIG. 1 of the drawing illustrates a guitar body anda portion of the neck thereof and shows how the invention of thisapplication may be incorporated into such an instrument.

A guitar body 2 has extending therefrom a neck 4 on which are mounted ina conventional fashion the usual frets 6. A rear string attachmentassembly 8 is provided on the body and anchors one end of each of aplurality of strings 10. In a preferred embodiment the strings areformed of steel and are electrically isolated from each other. In thiscase, the number of strings shown is six. Obviously, the number ofstrings can be varied for there are guitars that are in use which haveas many as 12 strings. The strings extend from the attachment assembly 8and pass over a bridge 12 which raises them from the surface of thebody. At their opposite ends the strings are secured by conventionaladjustable tensioning means mounted at the end of the neck, which meansare well-known in the art.

The guitar illustrated is of the type wherein the vibrations of thestrings are transduced into an electrical signal. For this purposepickups 14, 26 are provided adjacent the strings. The pickups areconstituted by coils wound around magnetized cores to as to produceelectrical signals responding to the vibrations of the strings whichelectrical signals may be amplified and converted into sounds bysuitable loudspeakers.

The guitar may be provided with volume and tone controls for the bassand treble portions of the musical spectrum as desired. Thus, a knob 16is arranged to controlthe volume of the rear pickup 26 while the knob 18controls the tone of its sounds. Likewise, a knob 20 controls the volumeof the forward pickup 14 while the knob 22 controls its tone. An outputjack 24 is provided on the side of thebody to receive a plug couplingthe pickup outputs to the amplifier.

What has been described heretofore, is the general configuration of aconventional electrically amplified guitar. In accordance with theinvention, the guitar is provided with a' differential pickup 26 of thetype designed to be insensitive to external magnetic fields. A magneticshield 28 surrounds the pickup 26 in a manner and for a purpose to beexplained in greater detail hereinafter. Positioned adjacent the neckbeneath the strings so as to be spacedfrom the pickup 26 are'the reardriver coil assembly 29 and the forward driver coil assembly 30. Aninput jack 32 is mounted on the side of the guitar body to receive aplug connecting the driving signals to the driver coil assemblies 29 and30. A first set of toggle switches 34 are provided in one row on thebody along with a second set of toggle switches 36 provided in a secondrow. Also'included is a master feedback toggle switch 38 along with achangeover switch 40. The purpose and function of these switches will beexplained hereinafter in connection with the explanation of the circuitshown in FIG. 7.

While the foregoing description has been thatof a guitar it iscontemplated that the invention may be applied to other stringedinstruments such as the harpsichord, or instruments utilizing steelprongs such as the electronic piano, and enhance their musical qualitiesas in the case in the guitar. Also, it is contemplated that where, as inthe embodiment of FIG. 1, the invention has been applied to each stringof the guitar but the pickups 14 and 26 mix the output of all thestrings and feed them into a common output, it may be found desirable toprovide a separate pickup for each-string, the output of which leadsinto a separate volume and tone control array and a separate amplifier,thus eliminating or controlling at will cross coupling or sympatheticvibration between strings. I

Referring now to FIG.2, there maybe seen a first embodiment of theinvention. This figure illustrates in diagrammatic form how theinvention may be applied in one form to any one or more strings ofastringed instrument. t

In this configuration a steel string 42 extends between two fixed points44 and 46 and is under tension I sothat it will vibrate to produce amusical sound when plucked or hit. Whether the string is in a guitar,piano, harpsichord orthe like the body of the instrument supports thestring to amplify the sound created by'its vibration and to produce aparticular tonal quality depending on the instrument.

In accordance with the invention a pickup 48 comprising a coil mountedon a magnetized core is positioned adjacent the string 42. As the string42 is vibrated as the result of being plucked or hit, an electricalsignal is generated in the pickup unit 48. An amplifier 50 has its inputconnected to the output of the pickup 48 and supplies the electricalsignal amplified to a driver unit 52. The driver unit consists ofa coilwound on an iron core and when excited by the amplifier produces amagnetic field which varies as the original vibration of the string andis effective to sustain that original vibration. In this configuration,and cmploying an amplifier with zero phase shift, the driving force isin phase with the strings fundamental frequency of oscillation astransduced by the pickup, the feedback in the loop (string, pickup,amplifier, driver) is positive, and oscillation is maintained as long asthe player permits the string to vibrate. In this form the inventioncould be used to play a drone or sustained note while a melody is playedon the other strings of the instrument. A switch 54 may be provided tobe manipulated by the musician to determine whether or not such asustained note is to sound and when its sound is to cease.

In another form of the invention, as illustrated in FIG. 3, the feedbackloop in addition to the pickup 48, amplifier 50 and driver 52 alsoincludes a harmonic selector 56. Such a harmonic selector may beconstituted by any of the passive or active filter circuits well knownin the art for deriving a desired harmonic or group of harmonics from anelectrical signal having a'fundamental frequency. Such circuits mayconsist-v of various combinations of resistance, inductance andcapacitance arranged to permit only a desired signal to be transmitted,or they may be more complicated frequency-independent active networks.

With the embodiment of this invention in FIG. 3 the driver 52 may besupplied with an electrical signal causing it to produce-a magneticfield varying in accordance with a harmonic component of the fundamentalvibration of the string 42. The effect under these circumstances is tocause the string to produce a musical sound much richer in that harmonicthan it would be under normal conditions.

In still another form of the invention another means of emphasizing theharmonic content of the signal supplied to thedriver 52 is shown; Inthis embodiment, the output of the amplifier 50 is supplied to a firstrectifier 58 poled either in one direction or a second rectifier 60poled in the opposite direction, or directly to the driver 52 via aterminal 62. A four position switch-64 is provided to be disposed in anoff position or toselectively connect the output of the amplifierthroughthe rectifier 58, terminal 62 or rectifier 60 to the driver'52.

When the switch64 isin the off position as shown, the feedback loop isinterrupted and the instrument is played in the conventional manner. Asdescribed previously, when the switch 64 is connected to the terminal 62and there is little or no'phase shift or waveformdi se tortion in thecircuit the effect of the feedback is to sustain the vibrationof thestring so as to produce .the fundamental note.

if the switch 64 is connected to the diode 53, the positive half cyclesof the amplifier output are supplied to the driver 52 and the effect hasbeen found to produce a vibration of the string wherein theeven-numbered harmonics predominate or appear to a greater extent. Onthe other hand, when the switch is connected to the rectifier 60 it hasbeen found that the odd-numbered harmonic content is increased.

The effects produced by the embodiments of FIGS. 3 and 4 can be combinedin the embodiment of FIG. 5. In this embodiment, the loop includes theharmonic sclector 56 as well as the oppositely poled diodes 58 and 60.Thus, the harmonic selector may be controlled to pass desired harmoniccomponents while the diode is chosen by operation of the switch 64 toemphasize either the oddor even-numbered harmonics or both.

FIG. 6 shows the pickups connected through a clipper 65 to theamplifier. The clipper turns the sine wave into a square wave and isthus a further method of enhancing the harmonic content of the signal.It also acts as a limiter to the amplitude of the strings vibrationunder feedback. 2

FIG. 7 illustrates an embodiment of the invention as applied to a guitarand which has proven satisfactory in use. The mode switches 36, theharmonic switches 34, along with the diodes 58 and 60, the driver coils156 and 158 and their cores 152 and 154 are duplicated six times, foreach of the six strings. In this embodiment, the pickup 48 is adifferential pickup of a type well known in the art, and is constitutedby a magnetized core 70 and a non-magnetized iron core 72, while on thecores 70 and 72 are a pair of coils 74 and 76, respectively. Themagnetized core 70 is adjacent to the strings, and transduces theirvibration into an electrical signal, while the non-magnetized core 72does not respond to the strings vibration. However, both coils respondto ambient magnetic fields identically. The coils are wound oppositely,so their difference signal is taken substantially cancelling ambientmagnetic fields, while retaining the signal from the vibrating string.In this way, direct pickup of the field from the driver coils isminimized, helping to eliminate unwanted feedback through the magneticfield in the air, an effect which can cause a very unpleasant howling,"analogous to that produced when a microphone is placed too close to aloudspeaker in a public address system. Further measures taken toeliminate feedback in the air loop are use of magnetic shielding 28about the differential pickup 26, and the enclosure of the driver coilsin an iron shielding box 160. Both of these are explained below.

Another pickup comprising a core 78 and coil 80 is also provided. Thepickup constituted by the cores 70, 72 and coils 74 and 76 isdenominated as the rear pickup and is that designated by referencenumeral 26 in FIG. 1. The pickup constituted by the core 78 and coil 80is denominated the forward pickup and is that designated by thereference numeral 14 in FIG. 1.

The output of the forward pickup is supplied to a potentiometer 82, theadjustment of which is controlled by the forward pickup volume controlknob 20 of FIG. 1. The output of the potentiometer derived by the wiper84 is connected to a tone control comprising a potentiometer 86, thewiper 88 of which is connected to one end of a capacitor 90, the otherend of which is grounded. The wiper 88 is controlled by the tone controlknob 22 in FIG. 1. The output of the rear pickup is supplied to apotentiometer 92 having a wiper 94 which connects its output to apotentiometer 96 connected in turn through its wiper 98 to a groundedcapacitor 100.

By adjustment of the wipers 84 and 94 the volume or amplitude of thesignals passed to the amplifier from the pickups may be controlled. Atthe same time the wipers of the tone control potentiometers may beadjusted to determine the frequency content of the signal transmitted.The potentiometers 86 and 96, together with their respective capacitors90 and 100, constitute what are called loser type tone controls, sincethey vary the amount of treble, or high frequencies, dumped through thecapacitor to ground. Since the forward pickup is situated near thevibrational antinodes of the fundamental frequency of vibration of thestring, the output of the forward pickup tends more toward the lower, orbass end of the musical spectrum. Conversely, the rear pickup issituated near the vibrational antinodes of the higher harmonics, andtends more toward the treble end of the spectrum. Thus, by suitablecombinations of adjustments of the forward and rear pickups volume andtone controls, a wide range of tones, i.e., harmonic balance, can beobtained.

The output of the pickups 14 and 26 is supplied via shielded conductors102 and 106 to terminals 104 and 108, respectively, of the changeoverswitch 40.

The center terminal 110 of this switch may be connected to either theterminal 104 or the terminal 108 or both of them to provide a signalinput to a feedback amplifier 112 and an audio amplifier 114. The audioamplifier'has its input, consisting of the signals from the forwardpickup, rear pickup, or from both connected to a loud speaker systemindicated by the reference numeral 116. The signal is supplied to theamplifiers via output jack 24 and split via shielded cables 111a andlllb.

The output of the feedback amplifier 112 is supplied via a conductor 118and input jack 32 to a terminal 120. As shown, the conductor 118 isshielded to minimize cross-talk and other interference. The terminal 120is connected to the master feedback toggle switch 38 which connects itin turn to a conductor 122 and a voltage divider constituted by a pairof resistors 124 and 126. An output is derived from the voltage dividerat the junction of the resistors 124 and 126 through a rectifier 128 andsmoothed by a capacitor 138 to ground to provide a gate control voltageto a triac 130. The voltage output of the divider is held relativelyconstant by a zener diode 132, the cathode of which is connected to thecathode of the diode 128 while its anode is connected through a resistor134 to ground. The gate control voltage of the triac is provided via aconductor 140 connected through resistor 141 to the appropriate string10. The strings are electrically isolated from each other. The circuitto the gate of the triac 130 is completed through the conductor 136connected to the frets 6 only when the appropriate string 10 is pressedinto contact with the frets 6 during the course of playing. Thus, inthis mode of operation, called the melody mode, the triac is made toconduct and supply the feedback signal to the string via its drivercoils only when that string is fretted. In this mode of operation, astrings vibration is fed back and sustained only if that string is beingfretted at the time; this mode eliminates unwanted feedback of openstrings, which may not be in key with the melody being played. This modeoccurs only when the mode switch for that string is in the melodyposition, as explained below. An alternative position of a mode switch36 is the drone position, in which a string sustains continuouslywhether it is open or fretted. This is also explained below.

The appropriate one of the six mode toggle switches 36 connects theconductor 122 to an off position 142 or a selected one of the terminals144 or 146. A conductor 148 connects the output of the mode switchingcircuit to the oppositely poled diodes 58, 60 and the terminal 62. Theappropriate one of the toggle switches 34, which may be termed theharmonic switches, conmeets the selected one of the rectifiers 58 or 60or terminal 62 via a conductor 150 to a driver constituted by a pair ofcores 152 and 154 on which are oppositely wound coils 156 and 158,respectively, connected in series but with opposite polarities so as toproduce oppositely directed magnetic fields.

The operation of this embodiment of the invention is as follows. Thestringed instrument, in this case a guitar, is played by plucking thestrings. The particular manner in which it is to be played is determinedby the musician by setting the switches in the position in which hedesires them and by adjusting the volume and tone controls also asdesired. Thus, if it is assumed that it is desired to play theinstrument wherein one of the strings performs the function of a drone,that is, produces a sustained note while a melody is played on the otherstrings, the toggle switch 38 is closed while the mode switch 36 forthat string is moved to contact the terminal 144. Assume further that itis desired that the drone sound be primarily produced by the fundamentalor lowest frequency components of the vibration of the string. Theharmonic switch 34 is then moved to contact terminal 62, while thechangeover switch 40 may be moved to contact the terminal 104. Inaddition, the tone control is adjusted by rotating the knob 22 so as tomove the wiper 88 along the potentiometer 86 towards the bass end of thetonal range. As the string is plucked, it vibrates generating anelectrical signal in the forward pickup which is derived by the wiper 84and supplied through the terminal 104 and switch 40 to the amplifier112. The output of the amplifier 112 is supplied through the conductor118, terminal 120, switch 38, conductor 122, switch 36, terminal 144,conductor 148, terminal 62 of switch 34 and conductor 150 to the drivercoils 156 and 158. The signal in the driver coils is effective to createan oscillating magnetic field which exerts a driving force on the stringto sustain its vibration. The particular arrangement just described isone wherein the string will tend to be driven by the lowest harmoniccomponent, i.e., the fundamental, so as to produce a pure drone sound.

If it is desired to utilize the instrument wherein the feedbackarrangement is effective to permit a string to play melody notes onlywhen that string is fretted, the mode selector switch 36 is moved to theterminal 146. Since these melodic notes are generally more pleasing whenvery rich in the higher overtones, the switch 40 may be moved to theterminal 108 and the tone control 18 adjusted to emphasize the treblecontents of the sound. In addition, the harmonic switch 34 is moved tocontact either rectifier 58, rectifier 60 or terminal 62, producing, inconjunction with the treble tone setting, even harmonics, odd harmonics,or both. In this way, all the previously described richness of sound isachieved. In this melody" mode, when the instrument is played, theoutput of the amplifier derived through the conductor 122 is supplied tothe triac 130 which will be rendered conductive when a string 10 ispressed against a fret 6 causing the appropriate voltage to appear atthe gate of the triac whereby it will conduct and will remain conductingfor as long as the string is held in contact with the fret, it being thenature of such devices to conduct as long as an anode is positive withrespect to a cathode. Thus, in the melody position, the string will bedriven only when it is fretted in the course of playing a melody,assuring that the open string does not sustain out of key.

Obviously, the arrangement shown in FIG. 7 permits a musician a widevariety of choices as to how the instrument can be played for thepermutations and the combinations of the various selectivelycontrollable switches and resistors is very large. The sounds that canbe created are varied and almost numberless. Basically, the arrangementprovides for an electromechanical feedback to the vibrating stringpermitting it to produce sound which are rich in harmonic content andmay be sustained or terminated as the musician desires.

In order to insure that the sounds produced are those desired by themusician, magnetic howling, that is, feedback in the air loop caused bydirect pickup of flux from the drivers by the pickups, must besuppressed. It is thus necessary to avoid the effect of stray flux froma driver acting on a pickup coil. This objective is achieved by acombination of measures. First, the driver and pickup coils are spacedfrom each other so as to lessen the direct magnetic coupling betweenthem. Secondly, within the rear pickup 26 the coils 74 and 76 are woundso that any signal produced by stray flux from the drivers is cancelledout and the signal represents solely the effect of the vibrating string,as previously described. In addition, magnetic shielding 28 is providedfor the rear pickup 26 consisting of layers of high and low permabilitymaterials. As may be seen in FIG. 1, the drivers 28 and 30 are spacedequidistant from the forward pickup l4 and their coils are wound inopposite senses as shown in FIG. 7 so that the field they exert at thelocus of the forward pickup 14 is substantially zero.

Further shielding is obtained as shown in FIG. 8 wherein the drivers aremounted in a shield box formed of magnetic ingot iron. A plurality ofwells 162 are provided in the iron shielding box and in each well ismounted a driver coil 166, the core 164 of which is mated to the bottomof the well. The upper face 168 of the core is provided with a concavefigure so as to focus or concentrate the flux generated on a string1,70. Suit able electrical connections are provided through the bottomof the shielded box so that the coils 166 may be connected to'thefeedback amplifier as desired.

As stated above, the invention may be used in conjunction with a widevariety of stringed instruments and when provided with the selectivelyoperated mode control indicated will permit the instrument to be playedin a large variety of keys. The location of the pickups and the driverson the instrument is determined by its physical configuration andtherefore the available space. The positioning of the elements is alsodetermined by the desire to eliminate or minimize any airloop feedbackbetween the drivers and the pickups.

Obviously, numerous variations and modifications beyond those discussedcan be made while still remaining within the scope of the invention andit is intended by the claims to cover all such modifications andvariations which fall within that scope.

What is claimed as new and desired to be secured as Letters Patent is:

l. A musical instrument including: a plurality of strings; meanssecuring each of the strings at their opposite ends to maintain them intension whereby they can be vibrated to produce a musical sound; atransducer in proximity with a string for generating an elec tricalsignal proportional to the vibration of the string as it is vibrated;means for amplifying the electrical signal so generated; the improvementcomprising driving means positioned adjacent the string for producing avarying magnetic field effective to vibrate the string; means forconnecting said driving means to said amplifying means to cause thestring to vibrate in response to the output of said amplifying means; avolume control resistor connected to the output of said transducer andto the input of said amplifying means; an adjustable impedance circuitconnected between said amplifying means and said resistor for passingdesired harmonic components of the electrical signal across saidresistor to said amplifying means; switching means for selectivelyconnecting and disconnecting said amplifier to said driving means; acontrollable bidirectional semiconductor switching device having a firstpair of terminals and a gate control terminal; means connecting one ofsaid first pair of terminals to said switching means and the other ofsaid pair of terminals to said driving means; and means including aswitch for selectively connecting and disconnecting said gate controlterminal to a source of gate control voltage.

2. A musical instrument as set forth in claim 1 wherein the movablecontact of said switch selectively connecting said gate control terminalto said source of gate control voltage is constituted by said string andthe fixed contact thereof is constituted by a fret.

3. A musical instrument as set forth in claim 2 including a pair ofoppositely poled rectifiers selectively connectable between saidswitching means and said driving meansv 4. A musical instrumentincluding: a plurality of strings; means securing each of the strings attheir opposite ends to maintain them in tension whereby they can bevibrated to produce a musical sound; a feedback circuit comprising atransducer in proximity with a string for generating an electricalsignal proportional to the vibration of the string as the string isvibrated; amplifying means having an input connected to the output ofsaid transducer; driving means positioned adjacent the string andconnected to the output of said amplifying means for producing a forceeffective to vibrate the string at frequencies and amplitudesproportional to those of the signal supplied thereto; means connected tothe said input of said amplifying means for controlling the amplitude ofthe said signal supplied to said driving means; and separate meansserially connected in said feedback circuit for modifying the frequencycontent of the signal supplied to said driving means.

5. A musical instrument as set forth in claim 4 wherein said separatemeans is connected between the output of said transducer and the inputof said amplifying means.

6. A musical instrument as set forth in claim 4 wherein said separatemeans comprises a rectifier connected between the output of saidamplifier and said driving means.

7. A musical instrument as set forth in claim 4 wherein said means forcontrolling the amplitude of the signal supplied to said driving meansis constituted by a volume control resistor connected to the output ofsaid transducer and said separate means is constituted by an adjustableimpedance circuit connected between said amplifying means and saidresistor.

8. A musical instrument as set forth in claim 4 wherein said separatemeans is constituted by a waveshaping circuit.

9. A musical instrument as set forth in claim 4 wherein said separatemeans is constituted by a harmonic selector.

10. A musical instrument as set forth in claim 5 including a rectifierconnected between the output of said amplifier and said driving means.

11. A musical instrument as set forth in claim 5 including a pair ofoppositely poled rectifiers connected between the output of saidamplifier and said driving means.

1. A musical instrument including: a plurality of strings; meanssecuring each of the strings at their opposite ends to maintain them intension whereby they can be vibrated to produce a musical sound; atransducer in proximity with a string for generating an electricalsignal proportional to the vibration of the string as it is vibrated;means for amplifying the electrical signal so generated; the improvementcomprising driving means positioned adjacent the string for producing avarying magnetic field effective to vibrate the string; means forconnecting said driving means to said amplifying means to cause thestring to vibrate in response to the output of said amplifying means; avolume control resistor connected to the output of said transducer andto the input of said amplifying means; an adjustable impedance circuitconnected between said amplifying means and said resistor for passingdesired harmonic components of the electrical signal across saidresistor to said amplifying means; switching means for selectivelyconnecting and disconnecting said amplifier to said driving means; acontrollable bidirectional semiconductor switching device having a firstpair of terminals and a gate control terminal; means connecting one ofsaid first pair of terminals to said switching means and the other ofsaid pair of terminals to said driving means; and means including aswitch for selectively connecting and disconnecting said gate controlterminal to a source of gate control voltage.
 2. A musical instrument asset forth in claim 1 wherein the movable contact of said switchselectively connecting said gate control terminal to said source of gatecontrol voltage is constituted by said string and the fixed contactthereof is constituted by a fret.
 3. A musical instrument as set forthin claim 2 including a pair of oppositely poled rectifiers selectivelyconnectable between said switching means and said driving means.
 4. Amusical instrument including: a plurality of strings; means securingeach of the strings at their opposite ends to maintain them in tensionwhereby they can be vibrated to produce a musical sound; a feedbackcircuit comprising a transducer in proximity with a string forgenerating an electrical signal proportional to the vibration of thestring as the string is vibrated; amplifying means having an inputconnected to the output of said transducer; driving means positionedadjacent the string and connected to the output of said amplifying meansfor producing a force effective to vibrate the string at frequencies andamplitudes proportional to those of the signal supplied thereto; meansconnected to the said input of said amplifying means for controlling theamplitude of the said signal supplied to said driving means; andseparate means serially connected in said feedback circuit for modifyingthe frequency content of the signal supplied to said driving means.
 5. Amusical instrument as set forth in claim 4 wherein said separate meansis connected between the output of said transducer and the input of saidamplifying means.
 6. A musical instrument as set forth in claim 4wherein said separate means comprises a rectifier connected between theoutput of said amplifier and said driving means.
 7. A musical instrumentas set forth in claim 4 wherein said means for controlling the amplitudeof the signal supplied to said driving means is constituted by a volumecontrol resistor connected to the output of said transducer and saidseparate means is constituted by an adjustable impedance circuitconnected between said amplifying means and said resistor.
 8. A musicalinstrument as set forth in claim 4 wherein said separate means isconstituted by a wave-shaping circuit.
 9. A musical instrument as setforth in claim 4 wherein said separate means is constituted by aharmonic selector.
 10. A musical instrument as set forth in claim 5including a rectifier connected between the output of said amplifier andsaid driving means.
 11. A musical instrument as set forth in claim 5including a pair of oppositely poled rectifiers connected between theoutput of said amplifier and said driving means.